This invention relates to plasma reactors and, in particular, to parallel plate plasma reactors.
As known in the art, the plasma reaction in a chamber, whether it be to deposit or remove material, is a complex balance of many parameters. It is recognized, for example in U.S. Pat. No. 4,473,436, that reactor geometry has an effect on the nature of an etch. Thus, not only must the gas or gas mixture, pressure, substrate temperature, power etc. be chosen with care, the design of the reactor chamber itself becomes a compromise among competing interests.
In the past, plasma reactors have been single function machines, at least outside the laboratory. Thus, for example, converting a frontside etch reactor to a backside etch reactor involved a substantial reconstruction of the machine, e.g. the lower electrode assembly in a parallel plate reactor must be modified or replaced.
While swapping sub-assemblies may seen feasible, one must consider their cost as well as the need to avoid corners, i.e. outside corners, pockets, i.e. inside corners, and gaps, all of which may deteriorate the performance of the reactor. In the case of parallel plate reactors, it is not practical to swap complete lower electrode assemblies due to the plumbing and electrical connections as well as the cost of machining the electrode.
Further, the materials used in the reactor chamber, or at least their surface finish, often required modification in order to accommodate various processes. When this is combined with the number of wafer sizes now in use, it is apparent that there is a large number of processes and wafer sizes confronting the manufacturer of plasma reactors. Yet, to reduce manufacturing costs, the proliferation of possibilities must somehow be accommodated. At the same time, the customer or user wants improved performance, e.g. better uniformity, higher etch rates, better anisotropy and/or selectivity. Thus, any change in the equipment to make it more flexible cannot reduce performance. In fact, if the change does not improve performance, it is unlikely that a customer would be interested in buying the reactor.
In view of the foregoing, it is therefore an object of the present invention to enable a single plasma reactor to be used for a variety of processes.
It is another object of the present invention to improve the etch rate of a plasma reactor.
It is a further object of the present invention to improve the uniformity of a plasma reactor.
It is another object of the present invention to simultaneously improve the flexibility and performance of a plasma reactor.